Material handling apparatus for delivering or retrieving items

ABSTRACT

A method and apparatus are provided for sorting or retrieving items to/from a plurality of destinations areas. The items are loaded onto one of a plurality of independently controlled delivery vehicles. The delivery vehicles follow a track that guides the delivery vehicles to/from the destination areas, which are positioned along the track. Once at the appropriate destination area, an item is transferred between the delivery vehicle and the destination area.

PRIORITY CLAIMS

The present application is a continuation of co-pending application U.S.patent application Ser. No. 13/631,817, filed Sep. 28, 2012, which is acontinuation of U.S. patent application Ser. No. 13/361,490 filed Jan.30, 2012 issued as U.S. Pat. No. 8,276,740 on Oct. 2, 2012, which is acontinuation of U.S. patent application Ser. No. 12/983,726 filed Jan.3, 2011 issued as U.S. Pat. No. 8,104,601, which is a continuation ofU.S. patent application Ser. No. 12/014,011 filed Jan. 14, 2008 issuedas U.S. Pat. No. 7,861,844, which claims priority to U.S. ProvisionalPatent Application No. 60/884,766 filed on Jan. 12, 2007. The presentapplication claims priority to each of the foregoing applications andthe entire disclosure of each of the foregoing applications is herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a material handling system for sortingor retrieving items. More specifically, the present invention relates toa material handling system incorporating a plurality of destinationareas arranged along a track for guiding a plurality of vehicles forcarrying items to and/or from the destination areas.

BACKGROUND OF THE INVENTION

Sorting documents and mail pieces manually is laborious and timeconsuming. For example, thousands of large organizations employ numerouspeople full-time to manually sort and deliver incoming and interofficemail and documents. For instance, a large company may receive 5,000 mailpieces that need to be sorted and delivered each day to differentdepartments and/or individuals. Such volumes require a significantnumber of employees dedicated to sorting and delivering the mail.Nonetheless, such volume is not typically sufficient to justify theexpense of traditional automated sorting equipment, which is quiteexpensive. Additionally, the mail for such organizations is typicallyquite diverse, which makes it more difficult, and therefore moreexpensive, to automate the sorting procedures.

Various systems for sorting have been developed to address the needs ofmail rooms for large organizations. However, the known systems sufferfrom several problems; the most significant are cost and size.Accordingly, there is a need for a compact and affordable automatedsorting system that is able to meet the needs of mid- to large-sizedorganization that handle several thousand mail pieces each day.

Similarly, may large organizations have extensive storage areas in whichnumerous items are stored. Sorting and retrieving items from thehundreds or thousands of storage areas requires significant labor toperform manually, and the known systems of automatically handling thematerials are either very expensive or have limitations that hampertheir effectiveness. Accordingly, there is a need in a variety ofmaterial handling applications for automatically storing and/orretrieving items.

SUMMARY OF THE INVENTION

In light of the foregoing, a system provides a method and apparatus fordelivering items to storage locations. The system includes a pluralityof storage locations, such as bins, and a plurality of delivery vehiclesfor delivering items to the storage locations or retrieving items fromthe storage locations. A track guides the delivery vehicles to thestorage locations.

In one embodiment, a controller controls the operation of the deliveryvehicles based on information determined for each item to be sorted.Additionally, the track may include a plurality of interconnectedvertical and horizontal sections so that the vehicles may travel along acontinuous path changing from a horizontal direction to a verticaldirection. Further, the vehicles may be driven such that the orientationof an item on the vehicle stays constant as the vehicles changes from ahorizontal direction of travel to a vertical direction of travel.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary and the following detailed description of thepreferred embodiments of the present invention will be best understoodwhen read in conjunction with the appended drawings, in which:

FIG. 1 is a perspective view of a sorting apparatus;

FIG. 2 is a plan view of the sorting apparatus illustrated in FIG. 1;

FIG. 3 is a fragmentary perspective view of the sorting apparatusillustrated in FIG. 1, shown without an input station;

FIG. 4 is a right side view of the sorting apparatus illustrated in FIG.3;

FIG. 5 is a front elevational view of the sorting apparatus illustratedin FIG. 3, shown without discharge bins;

FIG. 6 is a fragmentary sectional view of a loading station of thesorting apparatus illustrated in FIG. 1;

FIG. 7 is an enlarged fragmentary perspective view of a portion of theloading station of the apparatus illustrated in FIG. 3;

FIG. 8 is an enlarged fragmentary view of a portion of track of theapparatus illustrated in FIG. 1, showing details of a gate in an openposition;

FIG. 9 is an enlarged fragmentary view of a portion of track of theapparatus illustrated in FIG. 1, showing details of a gate in a closedposition;

FIG. 10 is an enlarged fragmentary perspective view of a portion of thetrack illustrated in FIG. 1, showing details of a gate;

FIG. 11 is an enlarged fragmentary perspective view of a portion of thetrack illustrated in FIG. 1, showing details of a gate, with the gateshown in an open position in phantom;

FIG. 12 is a top perspective view of a delivery vehicle of the apparatusillustrated in FIG. 1;

FIG. 13 is a plan view of the delivery vehicle illustrated in FIG. 12;

FIG. 14 is a right side view of the delivery vehicle illustrated in FIG.12;

FIG. 15 is a front elevational view of the delivery vehicle illustratedin FIG. 12;

FIG. 16 is a bottom perspective view of the delivery vehicle illustratedin FIG. 12;

FIG. 17 is a bottom view of the delivery vehicle illustrated in FIG. 12;and

FIG. 18 is an enlarged view of a wheel of the delivery vehicleillustrated in FIG. 12, shown in relation to the track of the sortingapparatus illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1-18, an apparatus for sorting items such asdocuments or mail pieces is designated generally 10. The apparatus 10includes a plurality of delivery vehicles or cars 200 to deliver itemsto a plurality of sort locations, such as output bins 190. At a loadingstation 310, each car 200 receives an item from an input station 50 anddelivers it to the appropriate bin.

The cars 200 travel along a track 110 to the sort locations. The trackhas a horizontal upper rail 135 and a horizontal lower rail 140, whichoperates as a return leg. A number of parallel vertical track legs 130extend between the upper rail and the lower return leg. In the presentinstance, the bins 190 are arranged in columns between the verticaltrack legs 130.

After a piece is loaded onto a car, the car travels upwardly along twopairs of vertical tracks legs and then horizontally along two uppertracks 135. The car 200 travels along the upper rail until it reachesthe appropriate column containing the bin for the piece that the car iscarrying. The track 110 includes gates 180 that fire to direct the car200 down the vertical legs and the car stops at the appropriate bin. Thecar 200 then discharges the piece into the bin.

After discharging the piece, the car 200 continues down the verticallegs 130 of the column until it reaches the lower rail 140. Gates fireto direct the car along the lower rail, and the car follows the lowerrail to return to the loading station 310 to receive another piece.

The cars 200 are semi-autonomous vehicles that each have an onboardpower source and an onboard motor to drive the cars along the track 110.The cars also include a loading/unloading mechanism 210, such as aconveyor, for loading pieces onto the cars and discharging the piecesfrom the cars.

Since the system 10 includes a number of cars 200, the positioning ofthe cars is controlled to ensure that the different cars do not crashinto each other. In one embodiment, the system 10 uses a centralcontroller 350 that tracks the position of each car 200 and providescontrol signals to each car to control the progress of the cars alongthe track. The central controller 350 may also control operation of thevarious elements along the track, such as the gates 180.

Input Station

At the input station 50, the mail pieces are separated from one anotherso that the pieces can be conveyed serially to the loading station 310to be loaded onto the cars 200. Additionally, at the input stationinformation is determined for each piece so that the piece can be sortedto the appropriate bin.

A variety of configurations may be used for the input station, includingmanual or automatic configurations or a combination of manual andautomated features. In a manual system, the operator enters informationfor each piece and the system sorts the mail piece accordingly. In anautomatic system, the input system includes elements that scan each mailpiece and detect information regarding each piece. The system then sortsthe mail piece according to the scanned information.

In an exemplary manual configuration, the input system includes a workstation having a conveyor, an input device, such as a keyboard, and amonitor. The operator reads information from a mail piece and then dropsin onto a conveyor that conveys the piece to the loading station 310.Sensors positioned along the conveyor track the piece as the conveyortransports the mail piece toward the loading station. An example of awork station having a conveyor for receiving dropped pieces and trackingthe pieces is provided in pending U.S. application Ser. No. 10/862,021,filed Jun. 4, 2004, which was published Jan. 27, 2005 under PublicationNo. U.S. 2005-0018214 A1 and which is incorporated herein by reference.The conveyor receives mail pieces dropped by an operator and tracks themail pieces as they are transported along the conveyor.

In an exemplary automatic configuration, the system includes an imagingstation, having an imaging device such as a high speed line scanningcamera. The imaging station scans each mail piece to detect informationregarding the destination for each piece. The system analyzes the imagedata to determine the destination information and then electronicallytags the mail piece with the destination and sorts the pieceaccordingly. An example of a system having an automated imaging stationfor scanning pieces as they are conveyed is described in U.S. patentapplication Ser. No. 09/904,471, filed Jul. 13, 2001, which waspublished Jan. 16, 2003 under Publication No. U.S. 2003-0014376 A1, andwhich is incorporated herein by reference.

FIGS. 1 and 2 illustrate such an automated system. The input stationincludes an input bin 55 for receiving a stack of mail. A feeder 60 inthe input bin serially feeds mail pieces from the input bin to aconveyor 65. An imaging station 70 positioned along the conveyor scansthe mails pieces as the pieces are conveyed to the loading station 310.The system 10 analyzes the image data to read information for the mailpiece, such as the recipient's address.

The conveyor 65 conveys the mail piece to the loading station 310. Atthe loading station the conveyor 65 conveys the mail piece onto a car200. As discussed further below, after the mail piece is loaded onto thecar, the car moves away from the loading station and another car movesinto position at the loading station to receive the next piece of mail.

In certain instances, the system may not be able to automaticallyidentify the relevant information for a mail piece. To process suchpieces, the system may include an operator to input the relevantinformation so that the mail piece can be sorted. For instance, thesystem may include an operator station having an input device and adisplay, such as a monitor. If the system cannot automatically determinethe address within a pre-determined time period, the system displays thescanned images for the mail piece to the monitor so that the operator atthe work station can view the images and manually enter the informationusing the input device.

In addition to the automated and manual systems described above, thesystem may be configured in a hybrid or semi-automated configurationhaving some operations performed manually and others automated. Forinstance, the system may include a manual input station that also has animaging station. Since the system can handle a wide variety of items, itmay be desirable to have an operator input the pieces manually so thatthe pieces are properly oriented and separated. The imaging station thenscans the items and processes the imaging data to determine the addressinformation for the pieces. Additionally, the operator station mayinclude an input device and a display for inputting information if theaddress for a piece cannot be automatically determined, as discussedabove. The operator can input the information as soon as the systemindicates to the operator that it cannot determine the information for apiece. Alternatively, as discussed below, the car may be directed to abuffer if the information for a piece cannot be determined. In such aninstance, the cars having such pieces will remain in the buffer whilethe system continues to process pieces for which the system candetermine the relevant information. The operator can continue tomanually drop pieces and wait until a number of pieces need manualkeying of information. The operator can then switch from the operationof dropping pieces to the operation of manually keying the pieces,sometimes referred to as local video encoding (LVE). The operator cancontinue keying until some or all of the pieces in the buffer have beensuccessfully coded, and then the operator can go back to the operationof manually dropping pieces. As yet another alternative, it may bedesirable to incorporate a separate operator station having the inputdevice and display so that one operator can input the mail at the inputstation and a separate operator can input the information for pieceshaving addresses that cannot be automatically determined.

As can be seen from the foregoing, the input station 50 may beconfigured in a wide range of options. The options are not limited tothose configurations described above, and may include additionalfeatures, such as an automated scale for weighing each piece, a labelerfor selectively applying labels to the mail pieces and a printer forprinting information on the mail pieces or on the labels.

Additionally, in the foregoing description, the system is described ashaving a single input station 50. However, it may be desirable toincorporate a plurality of input stations positioned along the system10. By using a plurality of input stations, the feed rate of pieces maybe increased. In addition, the input stations may be configured toprocess different types of items. In this way, each input station couldbe configured to efficiently process a particular category of items. Forinstance, if the system is configured to process documents, such asmail, one input station may be configured to process standard envelopes,while another input station may be configured to process larger mails,such as flats. Similarly, one input station may be configured toautomatically process mail by scanning it and automatically determiningthe recipient. The second input station may be configured to processrejects, such as by manually keying in information regarding therecipient.

Sorting Station

Referring to FIGS. 1-6, the system includes a sorting station 100, suchas an array of bins 190 for receiving the pieces. In the presentinstance, the sorting station includes a number of bins arranged incolumns. Additionally, the sorting station 100 includes a track 110 forguiding the cars 200 to the bins 190.

The track 110 includes a horizontal upper rail 135 and a horizontallower rail 140. A plurality of vertical legs 130 extend between theupper horizontal leg and the lower horizontal leg 140. During transport,the cars travel up a pair of vertical legs from the loading station 310to the upper rail 135 (as described below, the cars actually travel uptwo pairs of rails because the track includes a forward track and aparallel opposing track). The car then travels along the upper railuntil reaching the column having the appropriate bin. The car thentravels downwardly along two front vertical posts and two parallel rearposts until reaching the appropriate bin, and then discharges the mailpiece into the bin. The car then continues down the vertical legs untilreaching the lower horizontal leg 140. The car then follows the lowerrail back toward the loading station.

As can be seen in FIG. 2, the track 110 includes a front track 115 and arear track 120. The front and rear tracks 115, 120 are parallel tracksthat cooperate to guide the cars around the track. As shown in FIG. 13,each of the cars includes four wheels 220: two forward wheel and tworearward wheels. The forward wheels 220 ride in the front track, whilethe rearward wheel ride in the rear track. It should be understood thatin the discussion of the track the front and rear tracks 115, 120 aresimilarly configured opposing tracks that support the forward andrearward wheels 220 of the cars. Accordingly, a description of a portionof either the front or rear track also applies to the opposing front orrear track.

Referring to FIG. 18 the details of the track will be described ingreater detail. The track 110 includes an outer wall 152 and an innerwall 154 that is spaced apart from the outer wall and parallel to theouter wall. The track also has a back wall 160 extending between theinner and outer walls. As can be seen in FIG. 18, the outer and innerwalls 152, 154 and the back wall form a channel. The wheels 220 of thecar ride in this channel.

Referring to FIG. 11, the track includes both a drive surface 156 and aguide surface 158. The drive surface positively engages the cars toenable the car to travel along the track. The guide surface 158 guidesthe car, maintaining the car in operative engagement with the drivesurface 156. In the present instance, the drive surface is formed of aseries of teeth, forming a rack that engages the wheels of the cars asdescribed further below. The guide surface 158 is a generally flatsurface adjacent the rack 156. The rack 156 extends approximatelyhalfway across the track and the guide surface 158 extends across theother half of the track. As shown in FIGS. 11 and 18, the rack 156 isformed on the inner wall 154 of the track. The opposing outer wall 152is a generally flat surface parallel to the guide surface 158 of theinner wall.

As described above, the track includes a plurality of vertical legsextending between the horizontal upper and lower rails 135, 140. Anintersection 170 is formed at each section of the track at which one ofthe vertical legs intersects one of the horizontal legs. Eachintersection includes an inner branch 172 that is curved and an outerbranch 176 that is generally straight. FIG. 10 illustrates both aright-hand intersection 170 c and a left-hand intersection 170, whichare mirrors of one another. In FIG. 10, the intersections 170 c, 170 dillustrate the portion of the track in which two vertical legs 130intersect the upper horizontal leg 135. The intersections of thevertical legs with the lower rail incorporate similar intersections,except the intersections are reversed. Specifically, the point at whichvertical leg 130 c intersects the lower rail incorporates anintersection configured similar to intersection 170 d, and the point atwhich vertical leg 130 d intersects the lower rail incorporates anintersection configured similar to intersection 170 c.

Each intersection 170 includes a pivotable gate 180 that has a smoothcurved inner race and a flat outer race that has teeth that correspondto the teeth of the drive surface 156 for the track. The gate 180 pivotsbetween a first position and a second position. In the first position,the gate 180 is closed so that the straight outer race 184 of the gateis aligned with the straight outer branch 176 of the intersection. Inthe second position, the gate is open so that the curved inner race 182of the gate is aligned with the curved branch 172 of the intersection.

Accordingly, in the closed position, the gate is pivoted downwardly sothat the outer race 184 of the gate aligns with the drive surface 156.In this position, the gate blocks the car from turning down the curvedportion, so that the car continues straight through the intersection. Incontrast, as illustrated n FIG. 10, when the gate is pivoted into theopen position, the gate blocks the car from going straight through theintersection. Instead, the curved inner race 182 of the gate aligns withthe curved surface of the inner branch 172 and the car turns through theintersection. In other words, when the gate is closed, a car goesstraight through the intersection along either the upper rail 130 or thelower rail, depending on the location of the intersection. When the gateis opened, the gate directs the car from either a vertical rail to ahorizontal rail or from a horizontal rail to a vertical rail, dependingon the location of the intersection.

As can be seen in FIG. 11, the end of the gate remote from the pivotpoint of the gate flares outwardly so that the curved inner race matchesthe curved profile of the inner branch when the gate is open. As aresult, the gate has a generally L-shaped configuration. To accommodatethe flared end of the gate 180, the drive surface 156 of the innerbranch has a notch or recessed portion. When the gate is closed, thenotch provides clearance so that the outer race 184 of the gate liesflat, parallel with the drive surface of the outer branch 176. Further,in the example shown in FIG. 11, the gate is positioned along the upperrail 135 of the track 110. When the gate is closed, the recess in theinner branch of the intersection 170 allows the gate to lie flat so thatit is aligned with the drive surface of the upper rail.

In the foregoing description, the gates allow one of the cars to eithercontinue in the same direction (e.g. horizontally) or turn in onedirection (e.g. vertically). However, in some applications, the systemmay include more than two horizontal rails that intersect the verticalcolumns. In such a configuration, it may be desirable to include adifferent rail that allows the cars to turn in more than one direction.For instance, if a car is traveling down a column, the gate may allowthe car to turn either left or right down a horizontal rail, or travelstraight through along the vertical column. Additionally, in someapplications it may be desirable to allow the cars to travel upwardly,whereas in the system described above, the cars only travel downwardlythrough the sorting station. If the cars also travel upwardly in thesorting station, then the gates should be configured to accommodate andguide the cars when the cars travel upwardly through an intersection.

The gates 180 are controlled by signals received from the centralcontroller 350. Specifically, each gate is connected with an actuator186 that displaces the gate from the opened position to the closedposition and back. There may be any of a variety of controllableelements operable to displace the gate. In the present instance, theactuator 186 is a solenoid having a linearly displaceable piston.

In the foregoing description, the sorting station 100 is described as aplurality of output bins 190. However, it should be understood that thesystem may include a variety of types of destinations, not simply outputbins. For instance, in certain applications it may be desirable to sortitems to a storage area, such as an area on a storage shelf.Alternatively, the destination may be an output device that conveysitems to other locations. According to one example of an output device,the system may include one or more output conveyors that convey piecesaway from the sorting system toward a different material handling orprocessing system. For instance, an output conveyor designated A mayconvey pieces to a processing center designated A. Therefore, if a pieceis to be delivered to processing center A, the car will travel along thetrack to output conveyor A. Once the car reaches output conveyor A, thecar will stop and transfer the piece onto output conveyor A. Outputconveyor A will then convey the piece to processing center A. Further,it should be understood that the system may be configured to include aplurality of output devices, such as output conveyors.

In some embodiments, the system may include a plurality of outputconveyors in addition to the output bins. In other embodiments, thesystem may only include a plurality of output devices, such asconveyors, and the system is configured to sort the pieces to thevarious output devices. Further still, the system may be configured toretrieve pieces from storage locations. In such embodiments, the carsmay sort pieces to a storage location, such as a bin. Subsequently, oneof the cars may travel to the storage location and retrieve the itemfrom the storage location and transport it to one of the output devices.

One manner that the cars may retrieve items from the storage locationsis by including a conveyor at the storage locations. In this way, anitem at a storage location can be conveyed by the conveyor toward thetrack. When a car arrives at the storage location, the conveyor at thestorage location conveys the item onto the car, similar to the manner inwhich a piece is loaded onto the car at the loading column. Accordingly,the system can sort pieces to a plurality of output devices, in additionto sorting pieces to a plurality of storage locations beforesubsequently retrieving the pieces and conveying the pieces to theoutput devices.

As discussed above, the system is operable to sort a variety of items toa plurality of destinations. One type of destination is a bin; a secondtype is a shelf or other location on which the item is to be stored; anda third type of destination is an output device that may be used toconvey the item to a different location. The system may include one ormore of each of these types or other types of destinations.

Delivery Vehicles

Referring now to FIGS. 12-17, the details of the delivery vehicles 200will be described in greater detail. Each delivery vehicle is asemi-autonomous car having an onboard drive system, including an onboardpower supply. Each car includes a mechanism for loading and unloadingitems for delivery.

The car 200 may incorporate any of a variety of mechanisms for loadingan item onto the car and discharging the item from the car into one ofthe bins. Additionally, the loading/unloading mechanism 210 may bespecifically tailored for a particular application. However, in thepresent instance, the loading/unloading mechanism 210 is a conveyorbelt. Specifically, referring to FIG. 12, the loading/unloadingmechanism includes a plurality of narrow belts 212 that extend along thetop surface of the car. The conveyor belts are reversible. Driving thebelts in a first direction displaces the item toward the rearward end ofthe car; driving the belt in a second direction displaces the itemtoward the forward end of the car.

A conveyor motor 255 mounted on the underside of the car drives theconveyor belts 212. Specifically, the conveyor belts 212 are entrainedaround a forward roller 213 at the forward edge of the car, and arearward roller at the rearward edge of the car. The conveyor motor 255is connected with the forward roller 213 to drive the forward roller,thereby operating the conveyor belts.

The car includes four wheels 220 that are used to transport the caralong the track 110. The wheels 220 are mounted onto two parallel spacedapart axles 215, so that two or the wheels are disposed along theforward edge of the car and two of the wheels are disposed along therearward edge of the car.

Referring to FIG. 18, each wheel comprises an inner idler roller 224 andan outer gear 222 that cooperates with the drive surface 156 of thetrack. The idler roller 224 rotates freely relative to the axles, whilethe outer gear is fixed relative to the axle onto which it is mounted.In this way, rotating the axle operates to rotate the gear 222.Additionally, the idler roller is sized to have a diameter slightlysmaller than the distance between the upper wall 152 and the lower wall154 of the track. In this way, the idler roller may rotate freely withinthe track, while ensuring that the gear 222 of each wheel remains inoperative engagement with the drive surface (i.e. the teeth) 156 of thetrack. Accordingly, when the vehicle is moving horizontally, the rollerscarry the weight of the cart, while the gears 222 cooperate with thedrive surface 156 of the track to drive the vehicle along the track.

The car includes an onboard motor 250 for driving the wheels 220. Morespecifically, the drive motor 250 is operatively connected with theaxles to rotate the axles 215, which in turn rotates the gears 222 ofthe wheels. As shown in FIG. 16, the drive motor 250 is interconnectedto the axles 215 via a pair of drive belts 254 that are driven by thedrive motor.

The drive system for the car may be configured to synchronously drivethe car along the track. In the present instance, the drive system isconfigured so that each gear is driven in a synchronous manner.Specifically, each gear 222 is connected to an end of one of the axlesin a manner that substantially impedes rotation of the gear relative tothe axle. In this way each axle drives the attached two gears in asynchronous manner. Additionally, in the present instance, both axlesare driven in a synchronous manner so that all four gears are driven ina synchronous manner. There are various mechanisms that can be used tosynchronously drive the axles. For instance, a pair of drive motors canbe used to drive the axles, and the drive motors can be synchronized.However, in the present instance, a single drive motor 250 is used todrive both axles. Each axle includes a timing pulley 226 that is rigidlyconnected to the axle to prevent rotation of the pulley relative to theaxle. Similarly, a timing pulley 228 is connected to the motor shaft.The drive belt 254 connecting the timing pulley 226 on the axle with themotor is a timing belt so that the rotation of the drive motor isprecisely linked to the rotation of the axle. Although a single timingbelt can be used to drive both axles synchronously, in the presentinstance, a pair of timing pulleys is connected to the motor shaft, andeach timing pulley is connected to a corresponding timing pulley on oneof the axles, as shown in FIG. 16.

The drive motor 250 includes a sensor that is operable to detect therotation of the motor to thereby determine the distance the car hastraveled. Since the gears 222 are rigidly connected with the axles,which are in turn synchronously connected with the drive motor, theforward distance that the car moves corresponds can be exactlycontrolled to correlate to the distance that the drive motor isdisplaced. Accordingly, the distance that a car has traveled along thedetermined path depends on the distance through which the car motor isrotated.

To detect the rotation of the drive motor 250, the motor includes asensor 252 for detecting the amount of rotation of the drive motor. Inthe present instance the sensor 252 is a hall sensor. A portion ofrotation of the motor corresponds to what is referred to as a tick. Thesensor detects the number of ticks and sends a signal to the centralprocessor 350, which determines how far along the designate path the carhas traveled based on the known information regarding the path and thenumber of ticks that the sensor detects for the motor.

As the car travels along the track, an item on top of the car may tendto fall off the car, especially as the car accelerates and decelerates.Therefore, in the present instance, the car includes a retainer 230 toretain the element on the car during delivery. As illustrated in FIGS.12-17, the retainer 230 is a hold down that clamps the item against thetop surface of the car.

The retainer includes an elongated pivotable arm 232. A biasing element,such as a spring, biases the arm downwardly against the top surface ofthe retainer 230. The retainer 230 further includes an operator 234 inthe form of a tab. Pushing downwardly on the tab raises the clamp fromthe top surface of the conveyor to allow a piece to be loaded onto thecar or discharged from the car.

The car 200 may be powered by an external power supply, such as acontact along the rail that provides the electric power needed to drivethe car. However, in the present instance, the car includes an onboardpower source 240 that provides the requisite power for both the drivemotor 250 and the conveyor motor 255. Additionally, in the presentinstance, the power supply is rechargeable. Although the power supplymay include a known power source, such as a rechargeable battery, in thepresent instance, the power supply 240 is made up of one or moreultracapacitors. Ultracapacitors are extremely high energy densitycapacitors. Capacitors store electrical energy by physically separatingpositive and negative charges, in contrast to the chemical means abattery uses. Ultracapacitors rely on an electrostatic effect, which isphysical rather than chemical, and highly reversible. Theultracapacitors can accept very high amperage to recharge theultracapacitors. By using a high current, the ultracapacitors can berecharged in a very short time, such as a few seconds or less.

The car includes one or more contacts for recharging the power source240. In the present instance, the car includes a plurality of brushes245, such as copper brushes that are spring-loaded so that the brushesare biased outwardly. The brushes 245 cooperate with a charging rail inthe loading station to recharge the power source, as described furtherbelow.

Each car includes at least one and preferably two load sensors fordetecting the items as it is loaded onto the car. The sensor(s) ensurethat the mail piece is properly positioned on the car. In the presentinstance, the car includes a forward loading sensor 260 and a rearwardloading sensor 262. The forward loading sensor detects the leading edgeof the item as it is loaded onto the car. The forward loading sensor 260also detects the trailing edge of the item to ensure that the entirelength of the item is loaded onto the car. Similarly, the rearwardsensor 262 detects the leading edge and in certain instances, may detectthe trailing edge of the mail piece. The loading sensors 260, 262 may besimple I/R sensors that detect the presence or absence of a document ormail piece.

Although the car operates in response to signals received from thecentral controller 350, which tracks the location of each car, the carmay also include a reader 265 for reading indicia along the track toconfirm the position of the car. For instance, each bin may be assigneda unique bar code, and the forward reader may scan the track or otherarea around the bin 190 at which an item is to be delivered. The datathat the central processor has regarding the path that the car is tofollow and the data regarding the distance the car has traveled based onthe data regarding the rotation of the drive motor 250 should besufficient to determine whether the car 200 is positioned at theappropriate bin. Nonetheless, it may be desirable to double check thelocation of the car before the item is discharged into the appropriatebin. Therefore, the scanner may operate to scan and read informationregarding the bin at which the car is stopped. If the scanned dataindicates that the bin is the appropriate bin, then the car dischargesits item into the bin. Similarly, the car may have a second reader 266for reading indicia adjacent the rearward edge of the car. The secondreader 266 may be used in applications in which the system is set up toutilize a first series of bins 190 along the forward side and a secondseries of bins along the rearward side of the track 110.

In foregoing description, the cars have drive gears that interact withteeth in the track to guide the cars around the track. Additionally, asdescribed further below in the operation section, the location of thecar may be controlled based on information regarding how far the car hastraveled. In such applications it is desirable to synchronize the drivewheels of the car. However, in some applications alternative controlsystems may be used. For instance, the location of the cars can becontrolled based on signals from sensors positioned along the track orindicators positioned along the track. In such instances, the cars maybe configured to use a drive mechanism that is not synchronous asdescribed above.

As discussed further below, the car further includes a processor forcontrolling the operation of the car in response to signals receivedfrom the central processor. Additionally, the car includes a wirelesstransceiver so that the car can continuously communicate with thecentral processor as it travels along the track. Alternatively, in someapplications, it may be desirable to incorporate a plurality of sensorsor indicators positioned along the track. The car may include a readerfor sensing the sensor signals and/or the indicators, as well as acentral processor for controlling the operation of the vehicle inresponse to the sensors or indicators.

Loading Column

Referring now to FIGS. 6-7 the details of the loading column 300 will bedescribed in greater detail. The loading column 300 is formed adjacentthe output end of the input station 50. The loading column 300 is formedof a front pair of vertical rails 305 a, 305 b and a correspondingrearward set of vertical rails. The loading station 310 is positionedalong the loading column. The loading station 310 is the position alongthe track in which the car 200 is aligned with the discharge end of theconveyor of the input station 50. In this way, a mail piece from theinput station may be loaded onto the car as it is conveyed toward thecar from the input station.

Although the central processor 350 tracks the position of the car, ahome sensor 312 is positioned adjacent the loading station 310. When thehome sensor detects the car, the position for the car is known relativeto a fixed point along the track, and the central processor resets theposition of the car to the home or zero position.

Referring to FIG. 7, a pair of charging rails are disposed along thevertical rails 305 a, 305 b. The charging rails are conductive stripsconnected with an electrical supply. The charging contacts 245 of thecar 200 engage the conductive strips to recharge the ultracapacitors240. Specifically, the biasing element of the brushes 245 biases thebrushes outwardly toward the charging contacts. The electricity flowingthrough the charging contact 245 is a high amperage, low voltage sourcethat allows the ultracapacitors to recharge in a few seconds or less. Inaddition, since the power supply provided by the ultracapacitors lastfor only a few minutes, the car recharges each time it travels throughthe loading column.

Additionally, it may be desirable to incorporate a startup charging railsimilar to the charging rails described above, but disposed along eitherthe return rail or the rails in the column adjacent to the loadingcolumn, depending on where the cars are stored when the cars are shutdown. Since the cars use ultracapacitors, it is possible that theultracapacitors will discharge while the system is shut down. Therefore,upon startup the cars will not have any charge and will not be able tomove to the loading column to charge the ultracapacitors. Accordingly,the system may include a startup charging rail disposed along a railthat the cars contact when the cars are stored during shutdown. If thecars are stored in the loading column and the adjacent column duringshutdown, then the startup rail is disposed in the column adjacent theloading column. Alternatively, if the cars are stored on the return railand the loading column during shutdown, then the startup rail isdisposed along the return rail. In this way, when the system is started,a charging current is supplied to the cars through the startup chargingrail and the charging rail in the loading column.

As discussed previously, each car 200 includes a retainer 230 to holddown items on the car during transport. The retainer should be opened atthe loading station to allow an item to be loaded onto the car.Accordingly, as shown in FIG. 6, an actuator 316 is positioned along thecolumn. The actuator 316 projects inwardly toward the cars as the carsare conveyed up the loading column. As a car is conveyed upwardly in theloading column 300, the hold down actuator 316 contacts the hold downoperator or tab 236. The interaction between the actuator 316 and thetab 236 causes the retainer to open, so that items can be loaded ontothe car. As the car moves upwardly past the actuator 316, the tab 236 onthe car disengages the actuator, thereby releasing the retainer, therebyholding down or clamping the mail piece against the top surface of thevehicle.

In the foregoing description, the loading station has been described asa column in which an item is loaded onto the car and the car thentravels upwardly to the horizontal upper rail 135. However, in someapplications in may be desirable to configure the loading station sothat the items are loaded onto the cars at or near the top of thevertical column. In such an application, the load on the cars would bereduced since the car will not have to lift the item loaded on the car.In order to load the items on the cars at the top of the conveyor, avertical conveyor may be added to the system. For instance, a conveyorangled upwardly may convey the items upwardly to the top of the columnto load the items onto the cars. Alternatively, one or more of a varietyof conveyor configurations can be used to transport to items toward thetop of the loading column to load the items onto the cars.

Operation

The system 10 operates as follows. An item is processed at the inputstation 50 to identify a characteristic of the piece that is indicativeof where the piece should be sorted. For instance, the item may be amail piece that is to be sorted according to department, box number orrecipient. If the mail pieces are sorted by department, the piece may beprocessed to identify either an indicator of the department (such as boxnumber) or the piece may be processed to identify the recipient. Thecentral controller maintains a database that correlates various data toidentify the destination bin. For instance, the database may correlatethe recipient names with the appropriate department if the mail is beingsorted according to department. In other embodiments, the piece may be apart that has a product code and the database may correlate the productcode with the sort location.

As discussed previously, the input station may process the itemsautomatically or manually. In a manual mode, the operator manuallyenters information regarding a piece and then drops the piece on aconveyor. The system electronically tags the piece with the sortinformation and the conveyor conveys the piece toward the loadingstation. Alternatively, if the input system is an automated system, thepiece is automatically scanned to identify the relevant sortcharacteristic. For instance, the input station may use a scanner, suchas a bar code scanner to read the postnet code on a piece, or the inputstation may include an imaging device, such as a high speed line scancamera in combination with an OCR engine to read information on thepiece.

To prepare to receive an item, a car 200 moves along the track towardthe loading station 310 in the loading column 300. As the car approachesthe loading station, the operator 236 for the hold down 230 engages theactuator 316, which pivots the hold down upwardly to prepare the car toreceive an item, as illustrated in FIG. 6. When the car 200 moves intoposition at the loading station 310 the home sensor detects the presenceof the car and sends a signal to the central processor 350 indicatingthat the car is positioned at the loading station. In the followingdescription, the item being sorted is described as being a mail piece.It should be understood that such an item is an exemplary application ofthe system. As described above, the system can be configured to sort avariety of items in a variety of material handling applications.

Once the car is positioned at the loading station, the input stationconveys a mail piece onto the car. As the mail piece is being conveyedonto the car 200, the loading mechanism 210 on the car loads the mailpiece onto the car. Specifically, the input station conveys the mailpiece into contact with the conveyor belts 212 on the car. The conveyorbelts 212 rotate toward the rearward side of the car, thereby drivingthe mail piece rearwardly on the car.

The operation of the conveyor belts is controlled by the loading sensors260, 262. The forward loading sensor detects the leading edge of themail piece as the mail piece is loaded onto the car. Once the forwardloading sensor 260 detects the trailing edge of the mail piece, acontroller onboard the car determines that the mail piece is loaded onthe car and stops the conveyor motor. Additionally, the onboardcontroller may control the operation of the conveyor in response tosignals received from the rearward sensor 262. Specifically, if therearward sensor 262 detects the leading edge of the mail piece, then theleading edge of the mail piece is adjacent the rearward edge of the car.To ensure that the mail piece does not overhang from the rearward edgeof the car, the controller may stop the conveyor once the rearwardsensor detects the leading edge of the mail piece. However, if therearward sensor detects the leading edge of the mail piece before theforward sensor detects the trailing edge of the mail piece, thecontroller may determine that there is a problem with the mail piece(i.e. it is too long or two overlapping mail pieces were fed onto thecar. In such an instance, the car may communicate an error message withthe central controller, which may declare an error and provide anindicator to the operator that the car at the loading station requiresattention. Alternatively, a reject bin 325 may be positioned behind theloading station so that mail pieces on the car at the loading stationcan be ejected into the reject bin 325. In this way, if there is anerror loading a mail piece onto a car, the mail piece can simply beejected into the reject bin, and a subsequent mail piece can be loadedonto the car.

After a mail piece is loaded onto the car, the car moves away from theloading station. Specifically, once the onboard controller detects thata mail piece is properly loaded onto the car, the onboard controllersends a signal to start the drive motor 250. The drive motor 250 rotatesthe axles, which in turn rotates the gears 222 on the wheels 220. Thegears 222 mesh with the drive surface 156 of the vertical rails 305 inthe loading column to drive the car upwardly. Specifically, the gearsand the drive surfaces mesh and operate as a rack and pinion mechanism,translating the rotational motion of the wheels into linear motion alongthe track 110.

Since the cars move up the loading column from the loading station, thedestination for the car does not need to be determined until after thecar reaches the first gate along the upper rail 135. For instance, if anautomated system is used at the input station to scan and determine thecharacteristic used to sort the mail pieces, it may take some processingtime to determine the relevant characteristic. The time that it takes toconvey the mail piece onto the car and then convey the car up theloading column will typically be sufficient time to determine therelevant characteristic for the mail piece. However, if thecharacteristic is not determined by the time the car reaches the upperrail, the car may be directed down the second column, which is thecolumn next to the loading column. The car travels down the secondcolumn to the lower rail 140, and then back to the loading column. Thecar may stop in the second column to provide additional time todetermine the characteristic. However, after waiting for apre-determined period the system may declare that the address cannot bedetermined and the car may be advanced from the second column and thepiece may be discharged to a reject bin. Alternatively, rather thandeclare an error the car may continue to travel around the loop from theloading column to the second column until the characteristic isdetermined or until a predetermined time at which the central controllerdeclares an error. Additionally, rather than using the reject bin whenthe system is unable to determine the characteristic for a mail piece,one of the bins in the second column can also be used as a reject bin.In this way, the cars are ready to receive a mail piece as soon as thecar reaches the loading station, without having to eject the problemmail piece into the reject bin 325 at the loading station.

As described above, the system includes a loop that can be utilized as abuffer track to provide additional processing time to analyze thecharacteristic for the mail piece if necessary. Although the first andsecond columns can be used as the buffer loop, other columns can be usedas a buffer loop if desired.

The foregoing discussion described the process for buffering a car ifthe system is unable to determine the characteristic for the mail pieceby the time the car reaches the top rail. However, for most mail pieces,the system should be able to identify the characteristic without havingto buffer the car. The following discussion describes the operation ofthe system assuming that the characteristic for the mail piece isdetermined before the car reaches the upper rail 135.

Once the characteristic for the mail piece is determined, the centralcontroller 350 determines the appropriate bin 190 for the mail piece.Based on the location of the bin for the mail piece, the route for thecar is determined. Specifically, the central controller determines theroute for the car and communicates information to the car regarding thebin into which the mail piece is to be delivered. The central controllerthen controls the gates along the track to direct the car to theappropriate column. Once the car reaches the appropriate column the carmoves down the column to the appropriate bin. The car stops at theappropriate bin 190 and the onboard controller sends an appropriatesignal to the conveyor motor 255 to drive the conveyor belts 212, whichdrives the mail piece forwardly to discharge the mail piece into thebin. Specifically, the top of the car aligns with the gap between theappropriate bin 190 and the bottom edge of the bin that is immediatelyabove the appropriate bin.

As discussed above, the central controller 350 controls the operation ofthe gates 180 in response to the location of the car 200 and the routethat the car is to follow to deliver the mail piece. Additionally, asdiscussed below, the central controller controls the gates in responseto the position of other cars on the track.

As the car 200 travels along the upper rail 135 and approaches a column,the gates for the vertical rails 130 are controlled as follows. If thecar is to pass over the column on the way to the next column, the gatesare displaced into the closed position, as shown in FIG. 9.Specifically, both gates at the top of the column are closed so that theouter race 184 of the gate aligns with the straight track, with theouter race aligning with the drive surface 156 of the track 110. In thisway, the gates provide a straight drive surface that cooperates with thedrive surface 156 to allow the car to travel over the column.

When the car comes to a column that it is to turn down, the gates arecontrolled as follows. Referring to FIG. 5, the columns can be seenwithout the bins attached. The view in FIG. 5 is from the front of theapparatus 10, so the car will be traveling along the upper rail from theright to the left in the perspective of FIG. 5. In the followingdiscussion, the car is to be conveyed to a bin in the column designatedC in FIG. 5. Column C includes two pairs of vertical legs. The firstpair is front and back vertical legs 130 c on the left side of column C;the second pair is front and back vertical legs 130 d on the right sideof column C.

In order for the car to travel down column C, the wheels on the leftside of the car travel down legs 130 c and the right side wheels traveldown legs 130 d. Therefore, as the car approaches column C, the gates atthe top of 130 d are displaced to the closed position so that the leftside wheels remain on the upper rail and pass over the right side legs130 d. After the left side wheels of the car pass over the right legs130 c, the gates 180 at the top of the right legs 130 d are displacedinto the open position so that the right side wheels can turn down legs130 d. Specifically, after the left side wheels pass right legs 130 d,the central controller operates the solenoids 186 of the gates 180 atthe top of legs 130 to displace the gates into the open position, asshown in FIG. 8 (note that the view in FIG. 8 is taken from the rearside of the apparatus so that the perspective of the gates is reversedrelative to the front side). The gates 180 block the straight paththrough the intersection 170 and the curved inner race 182 of the gatesdirect the right side wheels down vertical legs 130 d. Similarly, thegates 180 at the top of the left side legs 130 c are displaced into theopen position to direct the left side wheels down vertical legs 130 c.

As the car approaches the intersections at the bottom of legs 130 c and130 d, the gates are operated similarly to the above description, but inreverse. Specifically, as the car approaches the intersections 170 atthe bottom of legs 130 c and 130 d, the gates 180 in the intersectionsare displaced into the opened position so that the gates direct theforward and leading wheels to turn down the lower rail. From theperspective of FIG. 5, the car travels from left to right after the carreaches the lower rail. After the car passes though the intersections atthe bottom of the rails 130 c, 130 d, the gates at the bottom of rightside legs 130 d are displaced into the closed position before the leftside wheels of the car reach the intersection at the bottom of the rightside legs 130 d. In this way, the left side wheels of the car passstraight through the intersection at the bottom of legs 130 d along thebottom rail 140.

As discussed above, the central controller 350 controls the operation ofthe gates in response to the position of the car and more specificallyin response to the position of the left hand and right hand wheels ofthe car. The gates are fired sequentially to ensure that the differentpairs of wheels are directed down the proper vertical legs.Alternatively, the operation of the gates may be controlled by signalsreceived from the cars. Specifically, the cars may include a transmitterthat transmits a signal to the central controller indicating that it isin proximity to a gate that is to be fired. Further still, the car mayinclude an indicator that may be scanned as the car approaches the gate.Based on the indicator and the know destination for the car, the gatemay fire. Still further, the car may include an mechanical actuator thatselectively triggers or actuates a gate to appropriately direct the car.

One of the advantages of the system as described above is that theorientation of the cars does not substantially change as the cars movefrom travelling horizontally (along the upper or lower rails) tovertically (down one of the columns). Specifically, when a car istravelling horizontally, the two front geared wheels 220 cooperate withthe upper or lower horizontal rail 135 or 140 of the front track 115,and the two rear geared wheels 220 cooperate with the correspondingupper or lower rail 135 or 140 of the rear track 120. As the car passesthrough a gate and then into a column, the two front geared wheelsengage a pair of vertical legs 130 in the front track 115, and the tworear geared wheels engage the corresponding vertical legs in the reartrack 120.

As the car travels from the horizontal rails to the vertical columns orfrom vertical to horizontal, the tracks allow all four geared wheels tobe positioned at the same height. In this way, as the car travels alongthe track it does not skew or tilt as it changes between movinghorizontally and vertically. Additionally, it may be desirable toconfigure the cars with a single axle. In such a configuration, the carwould be oriented generally vertically as opposed to the generallyhorizontal orientation of the cars described above. In the single axleconfiguration, the weight of the cars would maintain the orientation ofthe cars. However, when using a single axle car, the orientation of thesort locations would be re-configured to accommodate the verticalorientation of the cars. Similarly, the loading station would also bere-configured to load the pieces onto the cars in the verticalorientation.

Traffic Control

Since the system includes a number of cars 200, the system controls theoperation of the different cars to ensure the cars do not collide intoone another. In the following discussion, this is referred to as trafficcontrol.

A variety of methodologies can be used for traffic control. Forinstance, the traffic control can be a distributed system in which eachcar monitors its position relative to adjacent cars and the onboardcontroller controls the car accordingly. One example of such as systemutilizes proximity sensors on each car. If the proximity sensor for acar detects a car within a predefined distance ahead of the car, theonboard controller for the trailing car may control the car by slowingdown or stopping the trailing car. Similarly, if a car detects a carwithin a predefined distance behind the car, the lead car may speed upunless the lead car detects a car ahead of it within the predefineddistance. In this way, the cars may control the speed of the carsindependently based on the feedback from the proximity sensors.

Although the system may use a distributed system for traffic control, inthe present instance, the system uses a centralized system for trafficcontrol. Specifically, the central controller 350 tracks the position ofeach car 200 and provides traffic control signals to each car based onthe position of each car relative to adjacent cars and based on theroute for each car.

In the present instance, the central controller 350 operates as thetraffic controller, continuously communicating with the cars as the carstravel along the track 110. For each car, the central controllerdetermines the distance that each car can travel, and communicates thisinformation with the cars. For instance, if car B is following car Aalong the track, and car A is at point A, car B can safely travel to apoint just before point A without crashing into car A. As car A advancesto a subsequent point B along the track, car B can travel safely to apoint just before point B without crashing into car A.

The cars continuously communicate with the central controller to provideinformation indicative of their positions, so that the centralcontroller can continuously update the safe distances for each car asthe cars advance around the track.

Although the foregoing discussion is limited to determining safe zonesbased on the positions of the various cars on the track, thedetermination of safe zones is based on other factors that affect thetraffic. For instance, when calculating the safe distance for a car, thecentral controller considers the distance between the car and the nextgate, as well as the distance to the destination bin for the car.

As can be seen from the foregoing, increasing the frequency ofcommunication between the cars and the central controller increases theefficiency of the traffic flow along the track. Accordingly, in thepresent instance, the traffic control is designed to communicate with acar once for every inch the car travels along the track. Therefore, if acar travels at 25 inches per second, the central controller communicateswith the car every 40 msec. Further, it is desirable to have the carstravel at up to 50 inch/sec. Therefore, it is desirable to configure thecommunications to allow the cars to communicate with the centralcontroller every 20 msec.

In addition, to the foregoing variables used to calculate safedistances, information regarding the track profile ahead of each car isused to calculate safe distances. For instance, the central controllerdetermines whether the path ahead of a car is sideways movement, uphillmovement (i.e. movement vertically upwardly) or downhill movement (i.e.movement vertically downwardly).

One of the issues in traffic control relates to merging at intersections170. The problem arises when a car needs to merge onto the return rail140. If two cars will arrive at the intersection close enough tocollide, one of the cars needs to have priority and the other car needsto wait or slow down to allow the first car to go through.

A first method for controlling merging traffic is based on determiningthe next gap large enough for a car to have time to pass through anintersection without colliding with another car. In other words, if afirst car approaches an intersection and it is determined that the gapbetween the first car and a second car is not sufficient for the firstcar to pass through, the first car waits at the intersection until thereis a gap large enough to allow the first car to pass through.

A second method for controlling merging traffic is based on determiningwhich car is closest to the homing sensor at the loading station 310.The car with the shortest distance to the homing sensor gets priority atthe intersection.

Another factor that the traffic controller considers when calculatingsafe distances relates to the position of cars in adjacent columns. Inthe present instance, most of the adjacent columns share a commonvertical rail. For instance, in FIG. 5, the leftmost column usesvertical rails 130 a and 130 b. The column next to the leftmost columnuses vertical rails 130 b and 130 c.

However, in the present instance, some of the columns may have twovertical rails 130 that are independent from the adjacent columns. Forinstance, the loading column 300 has two independent rails that are notshared with the adjacent column. Therefore, cars can travel up theloading column without regard to the position of cars in the column nextto the loading column. Furthermore, as shown in FIG. 5, it may bedesirable to configure the column next to the loading column so that italso has two independent vertical rails. In this way, cars can morefreely travel up the loading column and down the adjacent column toprovide a buffer loop as described previously.

Accordingly, when calculating safe distances, the traffic controllerevaluates the position of cars in adjacent columns if the cars share acommon vertical rail to ensure that the two cars do not collide as thecar travel down the adjacent columns.

In the foregoing discussion, the sorting of items was described inrelation to an array of bins disposed on the front of the sortingstation 100. However, as illustrated in FIGS. 2 & 4, the number of binsin the system can be doubled by attaching a rear array of bins on theback side of the sorting station. In this way, the cars can deliveritems to bins on the front side of the sorting station by traveling tothe bin and then rotating the conveyor on the car forwardly to eject thepiece into the front bin. Alternatively, the cars can deliver items tobins on the rear side of the sorting station by traveling to the bin andthen rotating the conveyor on the car rearwardly to eject the piece intothe rear bin.

Additionally, the sorting station 100 is modular and can be readilyexpanded as necessary simply by attaching an additional section to theleft end of the sorting station. Further, although the foregoingdescribes the array of bins as being essentially a two dimensional arrayin which the cars simply travel in X and Y directions, the sortingstation can be expanded to add additional “runs” of track. Specifically,a separate sorting station parallel to or perpendicular to the sortingstation illustrated in FIG. 2 may be connected to the sorting station.In this way, the car would travel in a third dimension relative to the Xand Y directions of the sorting station illustrated in FIG. 2. Forinstance, additional sections of track may be connected to the sortingstation illustrated in FIG. 2 perpendicular to the illustrated sortingstation, so that the additional track forms an L-shape intersecting theloading column. In such a configuration, gates selectively direct thecars either down the upper rail 135 or rearwardly toward the additionaltrack. Similarly, a plurality of parallel rows of sorting stations canbe interconnected so that the cars selectively travel along a crossoverrail until the car reaches the appropriate row. The car then travelsdown the row until it reaches the appropriate column as described above.

It will be recognized by those skilled in the art that changes ormodifications may be made to the above-described embodiments withoutdeparting from the broad inventive concepts of the invention. Forinstance, in the foregoing description, the operation of the sortingstation is described as being centralized with the central controller.However, it may be desirable to have the cars control the operation ofthe gates. According to one alternative, the cars incorporate one ormore mechanical actuators that cooperate with an operator on the gate.The actuators on the cars are operable between first and secondpositions. In a first position, the actuator engages the gate operatorto displace the gate into the closed position. In a second position, theactuator engages the gate to displace the gate into the open position.Alternatively, the gate may be biased toward the opened position, sothat when the car actuator is in the second position it does not engagethe gate operator. In another alternative, each car includes a mechanismfor communicating with each gate. If the gate needs to be pivoted todirect an approaching car along a particular path, the car sends asignal to the gate indicating whether the gate should be opened orclosed. In response to the signal from the car, the gate pivots to theappropriate position.

Further, in the above description, the system uses a wirelesscommunication between the cars and the central controller. In analternative embodiment, a communication line may be installed on thetrack and the cars may communicate with the central controller over ahard wired communication link. Still further, the system has beendescribed as being useful in sorting incoming mail. However, the systemmay also be utilized to sort and prepare outgoing mail. For instance,after determining a characteristic for a mail piece, the system mayprint a marking onto the mail piece. For instance, after determining therecipient's address for a mail piece, the system determines which binthe mail piece is to be sorted to. As the mail piece is conveyed to thebin, a printer prints the appropriate postnet bar code on the piecebefore sorting the piece. To provide the printing functionality, thesystem may include a printer disposed along the track. When the carapproaches the printer the car stops and at least partially dischargesthe mail piece to extend the mail piece toward the printer. The printerthen prints the appropriate postnet code. The car then reverses theconveyors to load the piece back onto the car all the way, and thentravels to the appropriate bin. Similarly, the system may include adevice for selectively applying labels to the pieces. Similar to theabove example of printing markings onto the pieces, the labeler may bepositioned along the track. The cars selectively stop at the labeler onroute to the appropriate bin and at least partially discharge the mailpiece toward the labeler. The labeler then applies a label onto the mailpiece and the conveyor on the car then reverses to load the piece backonto the car.

In addition to outgoing mail applications, it may be desirable toincorporate a printer and/or a labeler in systems configured to processincoming mail. For instance, when sorting incoming mail pieces, it maybe desirable to print certain information, such as sort codes, a timestamp or audit trail information onto some or all of the pieces beingprocessed. In some instances such information may be printed directlyonto the mail pieces. In other instances, a label may be applied to themail pieces and the information may be printed on the label.

In addition to a printer and a labeler, the system may include a scalefor weighing the mail pieces. The scale may be positioned along thetrack 110, such as along the loading column. To weigh a piece, the carstops adjacent the scale, and ejects the piece from the car onto thescale by driving the conveyor belts 212. Preferably, the scale includesa conveyor or transfer mechanism for discharging the piece from thescale and back onto the car or onto a subsequent car. When the piece isloaded onto the car from the scale, the car drives the conveyors to loadthe piece as discussed above in connection with the loading station.

It should therefore be understood that this invention is not limited tothe particular embodiments described herein, but is intended to includeall changes and modifications that are within the scope and spirit ofthe invention as set forth in the claims.

What is claimed is:
 1. A material handling system, comprising: aplurality of destination areas; a plurality of delivery vehicles fordelivering items; a track for guiding the delivery vehicles verticallyand horizontally, wherein the destination areas are positioned along thetrack so that items can be transferred between the delivery vehicles andthe destination areas, wherein during operation, one or more of thedelivery vehicles are located on the track; a traffic controller forcontrolling the operation of the vehicles as the vehicles deliver itemsto the bins, wherein the traffic controller monitors the positions ofthe vehicles located on the track and calculates a safe distance foreach vehicle and communicates the safe distance to the vehicles, whereinthe safe distance for a vehicle corresponds to the distance that thevehicle can advance without interfering with another vehicle on thetrack; wherein the delivery vehicles receive the safe distance signalsfrom the traffic controller and advance along the track a distancecorresponding to the safe distance; and wherein the traffic controlleriteratively calculates safe distances for each vehicle as the vehiclesmove along the track and the vehicles advance along the track a distanceno further than the safe distance until receiving a subsequent safedistance from the traffic controller.
 2. The system of claim 1 whereineach vehicle comprises a transfer mechanism for transferring an itembetween the delivery vehicle and one of the destination areas.
 3. Thesystem of claim 1 wherein the traffic controller calculates a travelroute for each vehicle and each vehicle moves along the route.
 4. Thesystem of claim 3 wherein the safe distance for a respective one of thevehicles is a distance along the route for the respective vehicle. 5.The system of claim 1 wherein each vehicle comprises a wireless receiverfor receiving the safe distance signals wirelessly from the trafficcontroller.
 6. The system of claim 1 wherein the vehicles continuouslycommunicate a signal indicative of their positions wirelessly with thetraffic controller.
 7. The system of claim 1 wherein the track comprisesa plurality of gates for directing the vehicles from a vertical path toa horizontal or from a horizontal path to a vertical path.
 8. The systemof claim 1 wherein the traffic controller also bases the safe distancecalculation for a respective vehicle based on the distance between therespective vehicle and an intersection that the vehicle is directedtoward.
 9. The system of claim 8 wherein the traffic controller alsobases the safe distance calculation on a characteristic of the track onwhich the respective vehicle is to travel.
 10. The system of claim 8wherein the characteristic of the tracks include one or more ofhorizontal, upward or downward.
 11. The system of claim 1 wherein thetrack comprises a plurality of columns and adjacent columns share aportion of the track, wherein the traffic controller calculates the safedistance for a vehicle in one column based on the position of adifferent care in an adjacent column.
 12. The system of claim 1 whereinthe vehicles comprise drive elements having a plurality of teeth thatmesh with teeth in the track.
 13. A method system for transferring itemsbetween delivery vehicles and a plurality of destination areaspositioned along a track having horizontal and vertical sections,comprising the steps of: calculating a route for the one of the vehiclesto travel along the track to one of the destination areas; driving theone vehicle along the route to the one destination area, wherein thestep of driving the one vehicle comprises the steps of: monitoring thepositions of the vehicles on the track; determining a safe distance forthe one vehicle based on the positions of the vehicles on the track,wherein the safe distance is the distance that the one vehicle cantravel along the calculated route without interfering with anothervehicle on the track; communicating the safe distance with the vehicle;advancing the vehicle along the route no further than the safe distance;and as the vehicles move along the track, iteratively performing thesteps of determining the safe distance, communicating the safe distance,and advancing the vehicle; and transferring an item between the onevehicle and the one destination area.
 14. The method of claim 13 whereinthe one vehicle comprises an onboard transfer mechanism and the step oftransferring an item comprises using the onboard transfer mechanism. 15.The method of claim 13 wherein the step of communicating the safedistance comprises wirelessly sending a signal to the one vehicle. 16.The method of claim 13 wherein the step of monitoring comprises the stepof continuously communicating a position signal from the one vehicleindicative of the position of the one vehicle.
 17. The method of claim13 comprising the step of manipulating a gate to change the direction oftravel of the vehicle along the calculated route.
 18. The method ofclaim 13 wherein the step of calculating a safe distance is also basedon the distance between the one vehicle and an intersection that thevehicle is directed toward.
 19. The method of claim 13 wherein the trackcomprises a plurality of columns and adjacent columns share a portion ofthe track, wherein the step of calculating a safe distance comprisescalculating the safe distance for the one vehicle in one column based onthe position of a different vehicle in an adjacent column.